Which test question best shows restriction enzyme specificity?

Correct answer: Which enzyme recognizes which sequence

The direct answer is option A: which enzyme recognises which sequence. Specificity means that an enzyme does not cut every DNA molecule randomly. It recognises a particular short DNA sequence, called its recognition sequence or restriction site, and cuts at a defined position related to that site. To test specificity, one should therefore match each enzyme with the sequence it can recognise. Option A is correct because enzyme-sequence matching directly tests the molecular rule that determines where cutting occurs. Option B, asking which water is sweet, concerns taste and has no relation to DNA or enzyme recognition. Option C, asking which leaf is bigger, compares physical size and does not test a molecular recognition sequence. Option D, asking which stone is heavier, compares mass and is also unrelated to enzyme action. The word “specificity” is important: it means selective recognition, not merely that an enzyme can cut something. For example, an enzyme that recognises one sequence will not normally cut a different sequence under the same conditions. The exact recognition sequence depends on the enzyme. Exam cue: when specificity appears, look for the link between a particular enzyme and its particular DNA sequence.